This disclosure pertains to stage devices used for moving and positioning an object with extremely high accuracy and precision. Such stage devices are especially suitable for use in microlithography systems that perform transfer-exposure of a pattern, defined on a xe2x80x9cmaster platexe2x80x9d (mask, reticle, or the like, generally termed xe2x80x9creticlexe2x80x9d herein) onto an exposure-sensitive substrate (e.g., semiconductor wafer or the like). More specifically, the disclosure pertains to stage devices actuated by a linear motor and that perform highly accurate and precise movements and positionings while generating very low magnetic turbulence, and to microlithography systems including at least one such stage device.
Microlithography is a key technique used in the fabrication of microelectronic devices such as displays and semiconductor integrated circuits. Most current microlithography techniques utilize, as a pattern-transfer energy beam, a beam of deep ultraviolet (UV) light propagating through air at normal atmospheric pressure. These deep-UV techniques collectively are termed xe2x80x9coptical microlithography.xe2x80x9d
Other microlithography techniques currently under active development utilize any of various other types of energy beams such as xe2x80x9cextreme UVxe2x80x9d (xe2x80x9cEUVxe2x80x9d) radiation, X-radiation, and charged particle beams such as an electron beam or ion beam. Microlithography systems utilizing these alternative types of energy beams are being actively developed mainly because they offer prospects of substantially greater pattern-transfer resolution than obtainable with optical microlithography.
In any microlithography system, accurate and precise positioning of the reticle and substrate is extremely important for obtaining maximal pattern-transfer accuracy. Hence, the reticle and substrate are mounted to respective xe2x80x9cchucksxe2x80x9d on respective xe2x80x9cstages.xe2x80x9d The reticle stage and substrate stage generally are configured to move the reticle chuck and substrate chuck, respectively, in a respective X-Y plane relative to an optical axis extending in the Z-direction. For achieving such motions, the reticle and substrate stages include respective motors or analogous actuators.
Currently, most stage devices used in optical microlithography systems are so-called xe2x80x9cH-typexe2x80x9d or xe2x80x9cI-typexe2x80x9d X-Y stages. In both types of stages a movable guide extends in one of the X- and Y-directions between two parallel fixed guides that extend in the other of the X- and Y-directions. The respective chuck is mounted on a platform attached to a slider that moves along and relative to the movable guide. These types of stage devices are so-named because of the overall profile of the two fixed guides and the movable guide in the form of the letter xe2x80x9cHxe2x80x9d or the letter xe2x80x9cIxe2x80x9d.
Most recently, linear motors have become the actuators of choice for achieving stage motions in the X- and Y-directions. Use of linear motors desirably facilitates reducing the mass and size of each stage, and increases the operational efficiency of the stages. H-type stages are used mainly for substrate stages, which desirably have long respective movements (xe2x80x9cstrokesxe2x80x9d) in both of the X- and Y-directions. I-type stages are used mainly for reticle stages, which usually require a long stroke in only one of the X- and Y-directions, and thus have a relatively short stroke in the other of the X- and Y-directions.
For optical microlithography systems, since the energy beam can propagate readily through air at normal atmospheric pressure, the reticle and substrate chucks can be of the xe2x80x9cvacuum-suctionxe2x80x9d type. Also, the respective stages can be supported relative to a guide plate and on their guides by non-contacting xe2x80x9csingle-sidedxe2x80x9d fluid bearings (typically air bearings) that provide a high degree of freedom of motion when used with linear motors as actuators.
In contrast, charged-particle-beam (CPB) and extreme ultraviolet (EUV) microlithography must be performed in a vacuum environment because the beam is attenuated greatly in air at normal atmospheric pressure. As a result, reticle and substrate stages that utilize only single-sided fluid bearings (even if the bearings include vacuum-scavenging of bearing fluid) are not feasible, and movements along each guide must be supported by respective fluid bearings on all sides of the guide. The need to provide a respective fluid bearing on each side of the guide greatly complicates use of actuators such as linear motors for moving the stage platform relative to the guides.
As is well known, a linear motor has a xe2x80x9cstationaryxe2x80x9d portion, termed a xe2x80x9cstator,xe2x80x9d and a moving portion, termed a xe2x80x9cmover.xe2x80x9d In an H-type or I-type stage device, as described above, used as a reticle stage or substrate stage in a CPB microlithography system, both the stator and mover of at least one linear motor move along a movement guide. This motion of the entire linear motor causes problematic magnetic-field fluctuations (xe2x80x9cmagnetic turbulencexe2x80x9d) in the vicinity of the motor during operation of the stage device. Magnetic turbulence can perturb the trajectory of the beam and thus degrade the quality of microlithographic exposure.
The generation of magnetic turbulence from a conventional linear motor is shown schematically in FIG. 6, which is an elevational depiction. Two opposing permanent magnets 101, 102 of the stator are shown, situated laterally adjacent the trajectory of an electron beam EB. The trajectory is from top to bottom in the figure, and the permanent magnets 101, 102 of the stator are shown vertically aligned with each other beside the electron beam EB. The magnet 101 is disposed so that its S pole faces upward, and the magnet 102 is disposed so that its N pole faces upward. As a result, the respective N poles of each permanent magnet 101, 102, face each other. With such a disposition of the magnets 101, 102, the magnetic flux (dashed line) extending downward from the magnet 101 and the magnetic flux (dashed line) extending upward from the magnet 102 mutually repel and are diverted strongly to the left and right in the figure. Such strong lateral diversion of the magnetic flux causes the flux to reach the beam EB and cause distortion of the beam trajectory, which reduces the accuracy and precision of exposures performed with the beam.
In an actual CPB microlithography apparatus, the charged particle beam is contained in a xe2x80x9cbeam tubexe2x80x9d evacuated to a suitable vacuum, and the beam is deliberately deflected by magnetic fields produced by electromagnetic coils. The beam tube can be configured to provide some protection of the beam from stray magnetic fields from the external environment. Nevertheless, control and reduction of environmental and other stray magnetic fields around the beam tube is especially important in CPB microlithography. As evident in FIG. 6, an important source of stray magnetic fields is a nearby linear motor including permanent magnets arranged as shown in the figure. Whereas it is possible, using magnetic shields, to block stray magnetic fields produced by linear motors, this approach undesirably tends to add substantial complexity to the structure of the overall system.
In view of the shortcomings of conventional systems as summarized above, the present invention provides, inter alia, a stage device that can position an object (mounted to the stage) with high accuracy and precision, without causing magnetic-field turbulence.
A first aspect of the invention is set forth in the context of a stage device including a guide bar extending along a longitudinal axis, a slider slidably attached to the guide bar in a manner allowing the slider to slide relative to the guide bar along the longitudinal axis, and a stage platform connected to the slider. According to the first aspect, and in such context, actuators are provided for moving the stage platform in a direction parallel to the axis. An embodiment of such an actuator comprises a first linear motor situated on a first side of the guide bar and a second linear motor situated on a second side of the guide bar such that the first and second linear motors are situated in a bilaterally symmetrical manner relative to the axis. Each of the first and second linear motors comprises a respective stator and a respective mover. The respective stators extend parallel to the axis. The respective movers are attached to the slider such that energization of the first and second linear motors causes synchronous movement of the movers relative to the respective stators and thus movement of the slider along the guide bar in the direction of the axis.
In each linear motor the respective stator desirably comprises a respective yoke extending longitudinally parallel to the axis. The yoke is configured to define a channel opening extending parallel to the axis between first and second facing walls of the yoke. Each of the first and second facing walls has attached thereto a respective row of permanent magnets arranged opposite each other and that collectively define a coil-running gap extending parallel to the axis between the opposing rows. The permanent magnets in each row face the permanent magnets in the opposing row across the coil-running gap. The permanent magnets in each row have respective magnetic polarities arranged such that, in a transverse section perpendicular to the axis, the respective magnetic polarity of the permanent magnet on the first facing wall is attractively aligned with the respective magnetic polarity of the permanent magnet on the second facing wall. In a transverse section perpendicular to the axis, the respective magnetic polarities of the opposing permanent magnets on the first and second facing walls of the first linear motor desirably also are attractively aligned with the respective magnetic polarities of the opposing permanent magnets on the first and second facing walls of the second linear motor. Also, in each of the rows of permanent magnets, the magnets desirably are arranged with alternating polarity. By configuring the linear motors in the manner summarized above, magnetic fluxes produced by the permanent magnets are confined sufficiently so as to reduce substantially any leakage of magnetic flux from the stage device.
The yoke desirably has a U-shaped profile in transverse section perpendicular to the axis. In such a configuration, the channel opening is the opening in the xe2x80x9cUxe2x80x9d, and the first and second facing walls are the opposing ends of the xe2x80x9cUxe2x80x9d.
In each of the first and second linear motors, the respective mover desirably comprises a coil mounted to a respective coil-mounting member configured to position the coil in the respective coil-running gap of the respective linear motor. The coil-mounting members can be mounted to a slider plate that is mounted to the slider.
The first and second linear motors desirably apply respective drive forces, to their respective movers, that coincide with a center of gravity of the slider. Thus, pitch and yaw of the stage platform are reduced substantially during movement of the stage. As a result, stage scanning is improved, and the position of the platform is controllable with high accuracy during high-velocity scanning.
According to another aspect of the invention, stage devices are provided. An embodiment of such a stage device comprises a guide means, a slider means, a stage platform, and an actuator means. The guide means extends along a longitudinal axis. The slider means is slidably attached to the guide means in a manner allowing the slider means to move slidably relative to the guide means along the longitudinal axis. The stage platform is connected to the slider means. The actuator means, configured to move the stage platform in a direction parallel to the axis, comprises first and second stators extending parallel to the axis and situated on a first side and a second side, respectively, of the guide means in a bilaterally symmetrical manner relative to the axis. Each of the first and second stators has associated therewith a respective mover attached to the slider means. The movers are configured to exhibit synchronous movement relative to the respective stators, for effecting movement of the slider means along the guide means in the direction of the axis.
Possible specific configurations of the stators and movers of the actuator means are as summarized above.
According to another aspect of the invention, microlithography systems are provided. An embodiment of such a system comprises a reticle stage, an illumination-optical system, a substrate stage, and a projection-optical system. The reticle stage is configured to hold a pattern-defining reticle. The illumination-optical system is situated upstream of the reticle stage and is configured to direct an illumination beam onto a selected region of the reticle. The substrate stage is situated downstream of the reticle stage and is configured to hold an exposure-sensitive substrate. The projection-optical system is situated between the reticle stage and the substrate stage and is configured to direct a patterned beam from the illuminated region of the reticle to a selected imaging location on the substrate. At least one of the reticle stage and substrate stage comprises an actuator as summarized above, or is configured as a stage device as summarized above.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.